Method of Transferring Epitaxial Film

ABSTRACT

A method of growing an epitaxial film and transferring it to an assembly substrate is disclosed. The film growth and transfer are made using an epitaxy lateral overgrowth technique. The formed epitaxial film on an assembly substrate can be further processed to form devices such as solar cell, light emitting diode, and other devices and assembled into higher integration of desired applications.

RELATED APPLICATION DATA

The present application claims the benefit and is a divisional ofapplication Ser. No. 12/607,762 (now U.S. Pat. No. 8,193,078), which inturn claims the benefit under 35 U.S.C. 119(e) of the priority date ofProvisional Application Ser. No. 61/109,147 filed Oct. 28, 2008, both ofwhich are hereby incorporated by reference. The application also claimspriority to and is a continuation-in-part of Ser. Nos. 12/417931;12/417982; 12/418020 and 12/418223 also incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to epitaxial layer growth and transferusing liquid phase epitaxy and particularly to such systems/methods thatprovide one or more epitaxial layers that are stackable and connectablefor integration in monolithic devices, chip scale packaging, andmulti-component modules.

BACKGROUND

An epitaxial layer is the engine of compound semiconductor device whereits composition, dopant concentration, homostructure or heterostructure,and thickness determine a device's electrical, thermal, mechanical,and/or optical characteristics. Because of special material properties,compound semiconductors are critical to the success of many technologiesthat have demonstrated widespread applications in defense, space, andcommercial sectors. These applications and devices include but notlimited to optoelectronics such as lasers, sensors, optical datastorage, fiber optics, light emitting diodes (LED), and photovoltaics(PV), radio frequency (RF) and wireless systems, and microwave,millimeter-wave, radar, and satellite communication systems.

The prior art layer transfer methods separate grown epitaxy layer(s) orfinished device structure from a parent wafer substrate to a daughtersubstrate. The prior art process typically is practiced as follows:

-   -   1) Deposit a backside contact and back surface reflector atop an        inverted tandem structure which is grown on an etch stop layer        over a first substrate. Mount the inverted tandem structure        upside down on a second substrate. Remove the etch stop layer        and thus the first substrate. Complete frontside processing of        the tandem structure on the second substrate.    -   2) Deposit some layers on the first substrate, and other layers        on the second substrate. Polish and bond the two-layered        substrates by annealing. Detach the second substrate by a        hydrogen implantation, leaving the desired layer combination on        the first substrate.    -   3) Prepare a surface layer (surface conditioning) on a silicon        substrate. Grow device layer on the surface treated layer.        Attach a carrier to the device layer. Remove the surface layer        and the silicon substrate.    -   4) Build a semiconductor device layer on a first substrate.        Provide a set of first functional elements to connect in the        semiconductor device layer. Attach a carrier substrate on top of        the first functional elements. Remove the first substrate to        expose the bottom side of the semiconductor device layer        producing a first intermediate structure. Build a set of second        functional elements on a foundation substrate to produce a        second intermediate structure. Bond the first and the second        intermediate structures to form a third intermediate structure.        Remove the carrier substrate. Provide input output means on the        exposed surface of the first functional elements to form the        integrated device structure.    -   5) The epitaxial lift-off process allows the separation of a        thin layer of compound semiconductor material from the substrate        by strain-accelerated selective etching of an intermediate or        sacrificial layer. Other means of removing the sacrificial layer        in ELO include laser-assisted lift-off, ion bombardment.    -   6) Fabricate device on etch stop layer (epitaxial surface) grown        on a substrate. Mesa etch to etch stop layer and pattern        separate devices. Remove substrate using selective wet etching.        Bond the device onto a host substrate using a transfer        diaphragm.    -   7) Wax the top of the device. Lift-off in selective chemical        etch of a sacrificial layer and removes the substrate. Attach        the lift-off device to a glass substrate. Remove wax in        chemical.    -   8) Implant the device template substrate. Activate and clean the        surface of the device template substrate and the handle        substrate. Initiate the bond at room temperature. Apply uniform        pressure and heat to the stacked wafers to strengthen the bond        and initiate exfoliation.

These are just typical steps of course and are simplified here forinstructive purposes. Some background references for this technology areidentified below:

-   -   T. Kochiyaa, et al., “Anisotropy of lateral growth rate in        liquid phase epitaxy of InP and its association with kink-step        structures on the surface,” Applied Surface Science, 237, no.        1-4 (15 Oct. 2004): 235-241.    -   A. E. Nikolaev, et al., “SiC liquid-phase epitaxy on patterned        substrates,” Journal of Crystal Growth, 166, no. 1-4 (1 Sep.        1996): 607-611.    -   S. Sakai et al., “Selective Lateral Growth Mechanism of GaAs by        Liquid-Phase Electroepitaxy,” Japanese Journal of Applied        Physics, 33 (1994): 23-27.    -   K-W. Chung et al., “Lateral growth of GaAs over W by selective        liquid phase epitaxy,” Applied Physics Letters, 52 (1988): 1716.    -   D. Dobosz et al., “Epitaxial lateral overgrowth of semiconductor        structures by liquid phase epitaxy” International Journal of        Materials and Product Technology, 22, no. 1/2/3 (2005): 50-63.    -   Z. R. Zytkiewicz et al., “Recent progress in lateral overgrowth        of semiconductor structures from the liquid phase,” Crystal        Research and Technology, 40, no. 4-5, (2005): 321-328.    -   D. Dobosz et al., “Liquid phase growth and characterization of        laterally overgrown GaSb epitaxial layers,” Thin Solid Films,        412, (2002): 64.    -   Y. C. Liua et al., “Computational analysis of lateral overgrowth        of GaAs by liquid-phase epitaxy,” Journal of Crystal Growth,        275, (2005): 953-957.    -   Z. R. Zytkiewicz, “Epitaxial Lateral Overgrowth of GaAs:        Principle and Growth Mechanism,” Crystal Research and        Technology, 34, 5-6, (1999): 573-582.    -   M. Wanlass et al., “Monolithic, Ultra-Thin        GaInP/GaAs/GaInAsTandem Solar Cells,” NREL/PR-520-39852,        Presented at the 2006 IEEE 4th World Conference on Photovoltaic        Energy Conversion (WCPEC-4) held May 7-12, 2006 in Waikoloa, Hi.    -   M. S. Goorsky et al., “Engineered Layer Transfer Substrates for        Heterogeneous Integration of III-V Compound Semiconductors,”        2008 The International Conference on Compound Semiconductor        Manufacturing Technology.    -   R. Brendel, “Crystalline thin-film silicon solar cells from        layer-transfer processes: a review,” Proc. 10th Workshop on        Crystalline Silicon Solar Cell Materials and Processes, Aug.        13-16, 2000, Copper Mountain, USA.    -   M. M. A. J. Voncken et al., “Etching AlAs with HF for Epitaxial        Lift-Off Applications,” Journal of the Electrochemical Society,        151, no 5 (2004): G347-G352.    -   G. Roelkens et al., “Heterogeneous integration of III-V material        and Silicon: fabrication and devices,” Proceedings Symposium        IEEE/LEOS Benelux Chapter, (2004): 83-86.    -   N. M. Jokerst et al., “The Heterogeneous Integration of Optical        Interconnections Into Integrated Microsystems,” IEEE JOURNAL OF        SELECTED TOPICS IN QUANTUM ELECTRONICS, 9, no. 2, MARCH/APRIL        2003.    -   X. Y. Lee et al., “Thin Film GaAs Solar Cells on Glass        Substrates by Epitaxial Liftoff,” National renewable energy        laboratory and sandia national laboratories photovoltaics        program review meeting. AIP Conference Proceedings, 394, (1997):        719-727.    -   M. J. Archer et al., “Materials Processes for Ultrahigh        Efficiency Lattice Mismatched Multijunction Solar Cells,” SPIE        Optics+Photonics (2007): 6649-14.    -   P. Muller et al., “Surface melting of nanoscopic epitaxial        films,” Surface Science, 529, no. 1-2, (2003): 59-94.    -   J. J. Daniele, “Peltier-induced LPE and composition        stabilization of GaAlAs,” Applied Physics Letters, 27, no. 7,        (1975): 373.    -   J. J. Daniele et al., “Electroepitaxial (peltier-induced) liquid        phase epitaxy, compositional stabilization and x-ray analysis of        thick (120 μm) In1-xGaxP EPILAYERS ON (100) GaAs,” Journal of        Electronic Materials, 12, no. 6 (1983): 1015-1031.    -   U.S. Pat. No. 4,464,211 Logan et al.    -   U.S. Pat. No. 4,470,368 Reynolds, Jr. et al.    -   U.S. Pat. No. 4,768,463 Yoshida et al.    -   U.S. Pat. No. 4,186,045 Gatos et al.    -   U.S. Pat. No. 5,391,236 Dmitri et al.

All of the above are incorporated by reference herein.

A number of fundamental barriers persist to mass production andcommercialization of compound semiconductor devices namely: 1) materialcost, 2) substrate size, and 3) component/sub-system integration.Despite the fact that the manufacturing cost of compound semiconductorshas come down over time, it still remains much higher than silicon.Among the cost drivers, the cost of the crystalline substrate andepitaxial layer typically accounts for more than half of the finishedwafer cost. Depending on the type of materials, crystal or substratesizes also vary widely which raise challenges in tooling for waferprocessing to make discrete devices or integrated circuits.

The other barrier is a lack of a technology platform (fabrication andintegration platforms either monolithic or modular) versatile enough tointermix and integrate devices made from different materials for higherperformance and/or functionality. Examples of needs for such anintegration platform come from photonic integrated circuits in fiberoptics, full spectrum utilization multijunction cells in photovoltaics,and transceiver in communication and radar systems.

Although epitaxy growth technologies have advanced with sophisticationsin equipment, epitaxy structure, and materials over the past decades,the manufacturing process of monolithically layering over crystallinesubstrate, wafer processing for device or integrated circuit (IC)formation, device/IC packaging, and board/module assembly has remainedessentially the same.

Accordingly there is clearly a long-felt need for epitaxial systems andprocesses which are capable of addressing these deficiencies in theprior art.

SUMMARY OF THE INVENTION

An object of the present invention, therefore, is to overcome theaforementioned limitations of the prior art.

One aspect of the present invention concerns an assembly substrate thatcan be used to form a desired structure for an epitaxial layer;

Another aspect of the invention concerns an epitaxial structure thatincludes an assembly substrate and an integrated epitaxial thin filmlayer;

A further aspect of the invention concerns epitaxial layers andstructures that can be freely separated from associated seed substrates,allowing for re-use of such substrates and ease of later processing foradditional active devices;

Still another aspect concerns methods of making the aforementionedlayers, structures, as well as electrically active regions (P-Njunctions) and devices incorporating the same;

Another aspect concerns an apparatus that can be used to manufacture theabove referenced epitaxial films, structures, etc.

It will be understood from the Detailed Description that the inventionscan be implemented in a multitude of different embodiments. Furthermore,it will be readily appreciated by skilled artisans that such differentembodiments will likely include only one or more of the aforementionedobjects of the present inventions described herein. In particular, thepresent disclosure forms the basis of several distinct applicationscovering multiple separate inventions. Thus, the absence of one or moreof such characteristics in any particular embodiment should not beconstrued as limiting the scope of the present inventions.

While described in the context of an epitaxial film for integratedcircuit applications, it will be apparent to those skilled in the artthat the present teachings could be used in any number of other systemsin which it is desirable to improve an epitaxial packaging process.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram view of a preferred crystallinesubstrate, an assembly substrate, and a sacrificial layer or metamorphicbuffer layer grown on a crystalline substrate as building blocks forlayer growth and transfer in accordance with the teachings of thepresent invention;

FIG. 2 is a top view diagram of a preferred assembly substrate made inaccordance with the teachings of the present invention;

FIG. 3 is an illustration of a preferred method of growing andtransferring an epitaxy layer from a crystalline substrate to anassembly substrate by liquid phase epitaxy;

FIG. 4 is an illustrative diagram of various preferred forms of epitaxylayer at the completion of layer transfer;

FIG. 5 is a simplified diagram of the preferred growth of epitaxy layerby LPE.

FIG. 6 is an illustrative diagram of the preferred separation of thegrown epitaxy layer on an assembly substrate from the crystallinesubstrate;

FIG. 7 is an illustrative diagram of various preferred device structuresresulting from layer transfer and subsequent processing;

FIG. 8 is a simplified diagram of a preferred assembly substrate forlayer growth and transfer of heterojunction, multijunction, or diodestructure;

FIG. 9 is an illustrative diagram of two structures described in FIG.1and FIG.

8 that are brought into physical contact;

FIG. 10 is an illustrative diagram of the preferred growth of epitaxylayer on the combined structure in FIG. 9;

FIG. 11 is an illustrative diagram of the preferred preparatory stepsbefore the separation of the sacrificial layer or buffer layer from thecrystalline substrate or removal of the sacrificial layer;

FIG. 12 is a simplified diagram of the preferred epitaxy layer on theassembly substrate after the separation from the crystalline substrate;

FIG. 13 is a simplified diagram of the preferred formed device;

FIG. 14 is a top view diagram of FIG. 13.

DETAILED DESCRIPTION

The present invention addresses the aforementioned prior art barriersthrough a preferred simultaneous growth and transfer method of epitaxialstructures from a semiconductor substrate to an assembly substrate. Themethod lowers the material cost by replacing a conventionalsemiconductor substrate with a lower-cost assembly substrate and furtherusing a low-cost liquid phase epitaxy (LPE) manufacturing process.

Using the preferred method, the assembly substrate standardizessubstrate size for further processing regardless of the originalmaterial sizes. The epitaxial layer transferred directly unto anassembly substrate provides a unit building block for higher level ofdevice and subsystem integration. Unlike prior art layer transfertechniques, the present invention can preferably transfer an epitaxylayer during layer growth, which provides a number of benefits includinglow cost, high yield, high material quality, and wide applications.

LPE is a well-known method of growing a material epitaxially on asingle-crystalline substrate of a specific crystalline orientation,lattice constant, and defect density. Typically this techniques uses asolution of the material to make contact to and grow a thin layer (10 nmto 100 um) over a substrate surface. The thin layer grows and replicatesthe crystalline structure of the substrate as in seeded crystal growth.The growth process preferably begins with a melt of the materialsolution (or growth solution) in an appropriate solvent atsupersaturation that is maintained at an elevated temperature and acontrolled gas pressure. When the melt is brought into contact with thesubstrate, materials at the contact interface are in thermodynamicequilibrium at a constant temperature. At a lower but a constanttemperature, the material from the melt precipitates and growsepitaxially on the substrate of the same material (homojunction) until alayer of the desired thickness has been grown and the substrate isremoved from the melt.

Both growth rate and material composition of the epitaxial layer can becontrolled by temperature uniformity, responsive temperature profile,and gas pressure. In many applications, an impurity element (dopant) canbe added to a crystal lattice in low concentrations in order to alterthe optical/electrical/physical/chemical properties of the crystalmaterial. Therefore, a dopant can be added into the melt and the dopedlayer can be grown on an undoped substrate. To grow a heterojunction, amultijunction, or a diode structure, it may be necessary to grow asacrificial layer, a transition layer, or a metamorphic buffer layer ofgraded compositions and lattice constant on the crystalline substrate.The sacrificial layer or a transition layer may be removed from thecrystalline substrate during or after the subsequent growth of epitaxylayer unto an assembly substrate.

An epitaxial lateral overgrowth (ELO) technique uses LPE for preventingdefect propagation in forming multiple epitaxial layers (active layers)in microelectronic and optoelectronic devices. ELO is a process forgrowing an epitaxial layer on partially masked crystalline substrates.Typically, a buffer layer is grown first on the crystalline substrate.Then the crystalline substrate is covered by a thin film patterned withopenings or windows by conventional photolithography. Finally, theepitaxial layer is grown inside the openings on the crystallinesubstrate. The epitaxial layer initially nucleates on the surface of thecrystalline substrate and grows vertically from the crystallinesubstrate inside the masked openings. Once the layer growth reached thetop of the mask film, lateral growth begins along the masked filmsurface.

Depending on the orientation of masked openings relative to thesubstrate crystal orientation, the ELO technique can provide a fasterrate of growth for an epitaxial layer in the lateral direction overnarrow openings in a mask layer (such as silicon oxide or metal nitride)deposited atop a substrate than the growth of epitaxial layer in thenarrow openings in the vertical direction normal to the substratesurface. The result is typically a single epitaxial layer over the masklayer that is coalesced of lateral grown parts of the layers (wings)from adjacent openings.

Prior studies have shown that these ELO layers exhibit much lowerdislocation density than that in standard planar epitaxial layers grownon the crystalline substrate. For example, on (100) GaAs substrates theline seeds aligned at 15°, 30°, 60°, or 75° off from the <011> directionshow a large value of lateral to normal growth rate ratio. Other processparameters that may affect lateral growth of different materials includethe growth temperature dependence of the normal growth rate and thelateral growth rate in different crystallographic direction, electricfield through the growing layer, the amount of dopant introduced to themelt, the solubility of the dopant in the liquid solution, the spacingbetween windows, and physical properties of the growth solution such asviscosity as a function of temperature, fluid pressure, density, solutediffusion coefficient, etc.

Preferred embodiments of the present invention offer a transformationalepitaxy-level packaging (ELP) technique that advances beyond chip-scalepackaging (CSP) (where the resulting package is about the same size asthe die), wafer-level packaging (WLP) (where the package of integratedcircuit is at wafer level), and traditional package and assembly wherethe package of individual device is after wafer dicing. The preferredELP of the present invention leverages the ELO process using LPE andprovides a streamlined technique that can achieve high yield forepitaxial layer growth and layer transfer from a crystalline parentsubstrate directly unto an assembly daughter substrate.

The preferred embodiments of the invention can enable transformationalmaterial manufacturing and package integration for compoundsemiconductors with clear advantages in providing low cost, high yield,high quality materials, and wide applications over conventional methods.First, the preferred method can remove the traditional crystallinesubstrate of compound semiconductors to thus eliminate the cost ofcrystalline substrate in device. Furthermore, in most applications thecrystalline substrate can be re-used.

In addition, preferred embodiments of the invention also save packageand assembly costs at least in areas associated with wafer mount, waferthinning, wafer dicing, and die attach. Second, preferred embodiments ofthe layer transfer process can be made high yield by liquid-solid phaseseparation or localized etch in smaller areas that minimizes oreliminates defect-prone separation between two sheets of solids. Lastly,the ELP growth of the preferred embodiment produces high quality filmsof near-perfect material quality that is suitable for wide deviceapplications.

Differing from the prior-art layer transfer processes—which generallyfabricate the sacrificial or separation layer and an inverted devicestructure on the first substrate, bond to the second substrate, andremove the sacrificial or separation layer—preferred embodiments of thepresent invention provide a direct growth and attachment of an epitaxylayer to the second substrate (assembly substrate). Preferredembodiments of the present invention also do not need to resort tofabrication of an inverted device structure in subsequent processing.

The preferred embodiments of the present invention streamline packageand assembly steps by eliminating at least wafer mount, wafer thinning,wafer dicing, and die attach. These preferred embodiments provide awafer level platform where islands of different epitaxy materials canintermix on the same planar substrate. The preferred layer transfermethod of the present invention is easily integrable in liquid phaseepitaxy equipment for high-throughput and high-yield production.

Three main components are used in preferred embodiments of the presentinvention. First, a preferred multi-compartment boat apparatus is usedfor crystalline substrate, assembly substrate, manifold's aperture, andsource melt. Second, an assembly board is preferably made of materialsthat can withstand the thermal requirement of epitaxy growth and issuitable for end applications with patterned openings, slids, or windowsand other interconnects or components for epitaxy lateral overgrowth andsubsequent layer transfer. Third, a preferred layer transfer mechanismis used to separate a crystalline substrate and the assembly substrateduring or after layer growth, and utilizes both multi-zone temperaturecontrol from melt to crystalline substrate and mechanical actions.

FIG. 1 shows some of the basic building blocks used in an epitaxy layergrowth and transfer process. An upper graph (A) depicts a crystallinesubstrate 110 of any conventional semiconductor crystalline wafer. Asurface 115 of a crystalline substrate provides a two-dimensionalnucleation site for an epitaxy layer to replicate the lattice structureof the substrate for homojunction type growth. The crystalline substrate110 in some cases may not be a whole crystalline substrate but rathermultiple and localized nucleation sites on one substrate that match theopenings of a patterned assembly substrate.

Middle graph (B) depicts a crystalline substrate with a sacrificiallayer or a metamorphic buffer layer 120 grown atop it. The growth methodfor layer 120 can be of any conventional epitaxial growth method, suchas MOCVD, LPE, VPE, MBE, MOVPE, etc.

A sacrificial layer 120 is preferably of different material compositionfrom but lattice-matched to crystalline substrate 110. A metamorphicbuffer layer 120 includes graded compositions and a lattice constant tothe crystalline substrate. A sacrificial or a buffer layer 120 ispreferably used for growing heterojunction, multijunction, or diodestructures.

Sacrificial layer 120 may be removed in post-epitaxy growth to separatean assembly substrate from the crystalline substrate in case of transferof an epitaxy layer having a large surface to volume ratio. Bottom graph(C) shows an assembly substrate 130 with patterned holes, slits, orwindows 140 that are open through the thickness of the assemblysubstrate 130. A side profile of the holes, slits, or windows can bevertical or step recessed or sloped to any desired angle.

FIG. 2 is a top view diagrammatic of the assembly substrate 210illustrating different patterns, shapes, spacings, and sizes foropenings such as slits or windows 220 and holes or wells 230 for theinitial epitaxial growth in direction vertical to the crystallinesubstrate surface and later epitaxial lateral overgrowth. The assemblysubstrate 210 is preferably made of a solid, rigid material and can bethought of as a template or stencil for a desired epitaxial layergeometry, structure and arrangement for an integrated circuit. Theopenings in the assembly substrate define a multidimensional pattern tobe imparted to a thin film epitaxial layer. Accordingly the substrate isadapted to receive a liquid phase epitaxial material and has thermalcharacteristics sufficient to support growth of epitaxial materialwithin the openings without causing damage to the substrate that wouldprevent it from being used in subsequent conventional semiconductorprocessing steps for making active devices.

This substrate 210 is thus preferably a single or multi-layered ceramicsubstrate that is thermally matched to the thin single-crystal epitaxiallayer to be transferred onto or any substrate materials that has lowercost than the crystalline substrate and properties that fits specificproduct and application requirements. Accordingly other choices formaterials for substrate 210 will be apparent to those skilled in the artfrom the present teachings. A significant advantage of growing epitaxylayers on assembly boards of the present invention is that the latterthen can serve just like a conventional wafer for later processingsteps. It can be subjected to wafer processing for device/IC formation.It can save significant operational steps and costs in wafer mount,wafer thinning, wafer dicing, and die attach.

FIGS. 3A-3B illustrate a novel method of growing and transferring anepitaxial layer from a crystalline substrate with or without asacrificial layer or a buffer layer to an assembly substrate by liquidphase epitaxy (LPE). This mechanism generally employs a procedure bywhich an epitaxial apparatus 300 forms an epitaxial layer within anassembly substrate on top of a crystalline substrate, which is thenheated sufficiently so that it can be “swiped” or mechanically shearedoff the surface of the substrate.

In FIG. 3A a crystalline substrate 310 is preferably placed in a holderof apparatus 300, which preferably includes a platform (not shown) and arecessed base of a boat 320, which is preferably made of graphite orsimilar material. Graphite is a preferred material for materialavailablility in high purity form, being easily machined, and being notwet by metals. An assembly substrate 330 is preferably enclosed by abarrel or frames 370 preferably comprised of graphite or similarmaterial and placed atop crystalline substrate 310. It will beunderstood that other well-known mechanisms can be employed by apparatus300 to secure the assembly substrate/template and effectuate the goalsof the invention.

The LPE melt in a single or multiple melt pockets 350 preferably sitsstationary and the resulting melt is directed unto the assemblysubstrate 330 preferably through aperture's 360 in a manifold 365(preferably comprised of graphite or similar material) and thenultimately unto the surface of the crystalline substrate 310 throughopenings 340 in the assembly substrate. The form of LPE melt 350 cantake any number of forms commonly known in the art.

The manifold 365 may have one or more additional apertures 360 (notshown) and other conventional control mechanisms for controlling theoverall rate and amount of melt dispensed. For example the manifold maybe movable within apparatus 300 to dispense the melt across the surfaceof the assembly substrate. The melt dispensation is selective of meltpockets, time controlled, volume controlled, temperature controlled,location specific through the arrangement of manifold, and eitherstationary or motion controlled, for example, sliding, rotational, in ascanning motion, or any other moving mechanisms. The manifold aperturesthus define an aperture plate used by apparatus 300 to selectivelycontrol an area used for localizing the dispensing of the melt as well.

Other approaches are possible as well. For example the topology of themechanism could be inverted so that the assembly substrate is flippedwith the melt bath introduced into the bottom of the on the bottom ofthe boat 320. In some applications it may be possible to introduce themelt directly onto the crystalline substrate first, with the assemblysubstrate then physically pressed/superimposed on top of such melt so asto displace and force the bulk of the melt into openings 340 where itcan begin to crystallize. Residual material on the bottom of thesubstrate could be removed by any number of conventional mechanismswithout disturbing the resulting template in assembly substrate 330. Thegeometry/spatial relationship between the manifold 365 and assemblysubstrate 330 can be configured as well to optimize the distribution ofthe melt from chamber 350 to the desired openings 340. Accordingly otherorientations are possible, and all that is required is that there besome reliable mechanism for introducing the melt in a manner that allowscontrolled growth at a substrate interface at the bottom of openings340.

The zones where the crystalline substrate, the assembly substrate, andthe melt situate are situated are each preferably temperaturecontrolled. Initially, as seen FIG. 3A all three zones are preferably ofthe same temperature T₁ at or slightly above the bulk meltingtemperature of the melt. Control of the temperatures in these areas tocontrol the melt properties within apparatus 300 can be achieved by anynumber of well-known techniques. For example the entire assembly 300 maybe maintained in a temperature controlled chamber of a furnace, areactor, and/or conventional heat conduction and/or convectionmechanisms may be employed to provide localized heat energy to thesezones.

In FIG. 3B, an epitaxial layer 375 is formed when substrates 310 and 330and the localized melt 380 are slowly cooled to an end temperature T₂corresponding to a super-cooling point for the particular melt. At thistemperature segregation of solute from the melt results on thesubstrate, that is, the epitaxy layer 375 begins to grow. The entirelayer is then solidified over some predetermined time in a directionextending from the bottom of openings 340 to a surface of the assemblysubstrate 330. The time and temperatures required will be a function ofthe thickness of the epitaxial layer, the compositions of thesubstrates, etc., and can be determined experimentally using routineskill. In any event, the end result of this process is a completedepitaxial layer formed within the substrate/template 330 having adesired geometry, structure, material and doping composition suitablefor use in any conventional integrated circuit requiring such layers.

Apparatus 300 is further adapted so that preferably either or both thebarrel or frame 365 or the crystalline substrate holder 320 or both canbe physically moved with respect with one another. This allows for aswiping or shearing action that can be used to detach the completedepitaxial layer 375 from the underlying substrate 310 and allow it beintegrated as part of an additional semiconductor circuit.

Thus, as seen in FIG. 3C, during or after the epitaxial layer growth,the crystalline substrate holder 320 temperature is preferably raised toa surface pre-melting temperature T₃just below a re-melting temperatureof the bulk of epitaxial layer, which event causes epitaxial layer 375to begin to pre-melt by lattice heating at the epitaxiallayer-to-crystalline substrate interface, and in particular in thebottom of openings 340. It will be understood of course that othermechanisms for bringing about this pre-melt temperature can be employed,including by adding one or more heating elements embedded inside or aspart of the crystalline substrate holder and even the assembly substratebarrel or frames, a heat lamp inside or under the crystalline substrateholder, or a RF induction heated system applied to the crystallinesubstrate holder. Alternatively, a meshed heating element made ofresistance wires, a thin heating plate, a sheet of carbon nanotube, or athin film of positive thermal coefficient ceramic placed on top of thecrystalline substrate with openings for epitaxial growth unto theassembly substrate. Other examples will be apparent to those skilled inthe art.

At the same time (or after some predetermined time based on measuringthe pre-melt temperature, or some other time factor) apparatus 300employs a mechanical action to move barrel 370 and crystalline substrateholder 320 from each other to separate the epitaxial layer from thesurface of crystalline substrate. Mechanical actions may be swiping,sliding, rotation, spinning, pulling, tearing, vibration, stepping,breaking, cutting, or any combination (simultaneous or sequential)thereof. While a mechanical action serves to slide or shear theepitaxial layer 375 from the crystalline substrate 310, it will beapparent to those skilled in the art that other mechanisms may be usedto separate the two materials. For example in many instances the surfacearea of the epitaxial layer is relatively small compared to the overallsurface area so the amount of physical adhesion is relatively small. Insuch event it may not be necessary to employ any physical force to shearthe interface, and, instead, it may be possible simply to gradually liftthe assembly substrate 330 in a timed/controlled fashion (again using amechanical arm/fingers not shown) to achieve the same result in alift-off fashion.

At the completion of layer separation and transfer as illustrated inFIG. 3C, the temperatures of both the barrel and crystalline substrateholder are preferably lowered in apparatus 300 eventually toapproximately an ambient or room temperature T₄. More precise growthcontrol may be accomplished in some instances within apparatus 300 bymicro-heating and cooling elements in combination with or without aconventional Peltier-induced LPE in which an electric current (generatedby electric field or induced by magnetic filed) is passed through thesubstrate-melt interface and heats and cools it by a well-known Peltiereffect. The growth takes place at a constant temperature and growth rateis proportional to an applied current and/or applied field. Again othertechniques can be employed with the present invention.

FIG. 4 shows various forms of epitaxial layers after completion ofepitaxial layer growth and subsequent layer transfer from crystallinesubstrate 410 to an assembly substrate 430. FIG. 4A describes a discreteepitaxial layer in the openings of the assembly substrate, correspondingepitaxial lines of a desired width and configuration. FIG. 4B describesislands of a desired width and length forming an epitaxial layer on theassembly substrate. FIG. 4C describes a continuous epitaxial layer orfilm on the assembly substrate, again having a desired thickness.

FIG. 5 illustrates a growth of an epitaxial layer 575 by LPE incircumstances where there is an initial vertical growth 512 from acrystalline substrate 510 through the openings of an assembly substrate530 and subsequent lateral overgrowth of islands 525 on the surface ofthe assembly substrate. These islands may continue to grow laterally andcoalesce to form a single film 575, which may serve as the base foradditional epitaxial layers to grow on top thereof in subsequentprocessing operations. It will be apparent from these illustrations thatthe thickness, size, geometry and orientation of the epitaxialstructures (including islands, through-holes and lines) can becontrolled and configured in any manner of desired topology based on thecharacteristics of the assembly substrate.

In other embodiments it may be desirable and/or feasible to controlcompositional variations within the epitaxial layer, such as by addingdoping and/or structural gradients. To do this the melt compositioncould be varied by time so that at a first time a particular meltcomposition/doping is added, while at a subsequent time a different meltmix (with different composition/doping) is added. Again the process canbe automated to create graded epitaxial layers of any desired chemical,physical and electrical properties as needed for any particularapplication. In other instances the assembly substrate could be used toassist in tailoring the epitaxial film characteristics, including byphysical configurations and other variations for altering the filmgrowth and/or composition.

FIG. 6 illustrates generally the separation of a grown epitaxial layer675 on an assembly substrate 630 from a crystalline substrate 610. Asnoted earlier the separation may take place during epitaxial layergrowth or after epitaxial layer growth by a combination of temperatureand mechanical means as described in FIGS. 3A-3C.

FIGS. 7A-7D illustrate how the invention's techniques can be used tomanufacture more complex epitaxial structures. These device structuresinclude epitaxial layers 775 with additional processing steps andpatterned layers 720. As is apparent from FIG. 7, the number ofadditional epitaxy layers, epitaxy islands or continuous epitaxy layers,post-epitaxy processing steps, device structures, device layout,dimensions, and patterns can be varied as desired for different productsand applications. In particular the invention can be used for makingdevices which include:

-   (A) single junction-   (B) double junction or multi-junction (monolithic)-   (C) double junction or multi-junction (hybrid)-   (D) single junction, double junction or multi-junction within    openings

In FIG. 7A a single junction or homojunction device can be formed withone continuous layer on the assembly substrate 730. An active region(e.g. p-n junction) 715 may be formed after the epitaxial layercompletes an initial lateral overgrowth forming a continuous layer.Thereafter a p-n junction 715 may be grown using conventional processingtechniques. In general the completed epitaxy-on-assembly substrate isadvantageous because it can be used for post-epitaxy processing like anywafer fabrication for device and/or integrated circuit formation. Thesize and thickness of the assembly substrate can also be made to matchthat of any semiconductor wafer that fit into the wafer fabrication andhandling.

In FIG. 7B a second continuous epitaxy layer 776 is manufactured on thesurface of an underlying first epitaxial layer 775. Thus an epitaxiallayer can be grown on an assembly substrate (instead of the crystallinesubstrate). In this manner the assembly substrate 730 can now serve asthe base for double or multi-junction active layer formationmonolithically through another LPE or even by any conventional epitaxygrowth means.

FIG. 7C provides an alternate method to form double junction ormulti-junction layers that is not purely monolithic but instead part ofa hybrid package or a modular integration that may consist of stackingof multiple device assembly layers intermixed with multiple epitaxylayers and/or different localized pockets of epitaxy materials anddevices of different functionalities. As seen therein, a first assemblysubstrate 730 containing a first epitaxial layer 775 is formed, followedby a second assembly substrate 730′containing a second epitaxial layer776′. Again the composition and properties of the layers can be tailoredas needed for any function.

FIG. 7D describes yet another scheme of forming single junction, doublejunction or multi-junction within the openings of an assembly substrate730 such that discrete devices (shown as stacked layers of activedevices 715 and epitaxial layers 775, 776) can be formed, assembled, andseparated by cutting directly the assembly substrate in the area notedwith a hash marks 780.

FIG. 8 is a simplified diagram of another embodiment of an assemblysubstrate 830, including other preferred novel features such as a mesh(and/or a patterned plate as shown in FIG. 2) 805, a patterned adhesionlayer 825, cavities 835, and a plate 838 to cover cavities, prior tomaking contact to a crystalline substrate 810 with a sacrificial layer820. Except where noted like reference numerals are intended tocorrespond with similarly referenced components identified above inprior figures. Thus the assembly substrate 830 can be of a one ormulti-layered ceramic substrate that is thermally matched to the thinsingle-crystal epitaxial layer to be transferred onto or any substratematerials that has lower cost than the crystalline substrate andproperties that fits specific product and application requirements.

The adhesion layer 825 can be of a metallic film, an organic film, or anadhesive tape. The adhesion layer may be necessary for cases when theepitaxy layer surface-to-volume ratio is large, the thickness ofassembly substrate is much thicker that the epitaxy layer, or theepitaxy layer is grown and attached directly to the backside, thesurface that contacts the epitaxy layer first during growth, of theassembly substrate.

The assembly substrate 830 can have patterned openings 870 and otherdevices or components previously formed. Epitaxial layer transfer may beaccomplished through thermal and/or mechanical means as described inFIG. 3. The embodiment of FIGS. 8-13 uses an etchant to help detach theepitaxial layer, rather than primarily heat/mechanical means. In thisinstance of using an etch to accomplish layer transfer, cavities 835 areused for guiding etchant to remove sacrificial layer after epitaxialgrowth and the plate 838 is used to cover cavities 835 during epitaxialgrowth. Therefore the purpose of plate 838 is to prevent theintroduction of material in these cavities during this depositionoperation. Instead, as seen in FIG. 8, openings 870 are areas whereepitaxial growth takes place. The patterned plate 805 may have specialoptical, electrical, mechanical and/or other properties that suit thedevice applications. For example, the plate may be of glass, acrylic,other transparent, beam collection, or beam steering media for the solarcell application.

FIG. 9 shows additional novel feature of a preferred spacer 901 when theepitaxy layer is to be grown and attached directly to the backside of adevice, the surface that contacts the epitaxy layer first during growth,The contact on either side can be patterned, interlocked, or formed witha spacer 901 to open up the space for subsequent epitaxial film growthand required thickness. The spacer 901 may be deposited directly on thesacrificial layer or the crystalline substrate such as a patternedsilicon nitride thin film or other materials of thin layer. The spacermay also be a patterned sheet or plate that makes physical contact tothe surface of sacrificial layer or the crystalline substrate. The useof different types of spacers therefore can be used to configure/alteran epitaxial layer geometry and arrangement on an underlying substrate.

FIG. 10 is an illustrative diagram showing the preferred growth ofepitaxial film 1075 on the crystalline substrate 1010 or on asacrificial layer or buffer layer 1020 through the patterned openings ofthe assembly substrate. The crystalline substrate 1010 and the assemblysubstrate 1030 can be positioned in particular orientations to best fitthe epitaxial growth apparatus and growth conditions. As with FIG. 8 aplate 1038 covers cavities 1035. Epitaxial lateral overgrowth (ELO) canbe implemented by applying a heating element or mask placed on top ofcrystalline substrate 1010. Otherwise, ELO usually does not apply togrowth directly on the crystalline substrate because the growth occursin the vertical direction perpendicular to the surface of thecrystalline substrate.

FIG. 11 is an illustrative diagram showing the later removal of plate1138 covering cavities 1135 and spacer 1101. Sacrificial layer or bufferlayer 1120 can be removed by a combined thermal and mechanical means asdescribed previously in FIG. 3 or by other physical, chemical, ionicbombardment, thermal, mechanical, electromechanical, optical means, or acombination thereof. In a preferred approach using a chemical process, aselective etchant can be applied onto the sacrificial layer 1120 throughthe cavities 1135 and/or an edge portion 1150. The details of the etchchemistry recipe can be determined using routine skill based on thecomposition of an underlying substrate, sacrificial layer 1120,epitaxial film 1175, etc.

FIG. 12 is a simplified diagram of the completed epitaxial film 1275 asit may be employed on the backside of an assembly substrate as part ofan electrically active region to be used with integrated circuits. Theassembly can be further processed with additional epitaxy layers,processing steps, and patterned layers 1212 that may includemetallization, thin film etching. film deposition, and/or encapsulationto form desired devices such as solar cell, light emitting diode, andother integrated circuits for a desired applications.

FIG. 13 is a simplified diagram of a completed device 1300 that isseparated by means of saw, scribe and break, or chemical etch. Theseparated discrete device 1300 on assembly substrate 1330 can be furtherprocessed and/or assembled with final dimensions with additionalcomponents 1312. The assembled package can be further incorporated intoa module or higher integration as desired.

FIG. 14 is a diagram of a top view of FIG. 13 illustrating some keyconstituents such as patterned assembly substrate 1430, components 1412on assembly substrate 1430, epitaxial film 1475, and patterned layers ordevices 1432 on the epitaxial film 1475.

Other examples will be apparent to those skilled in the art and it isexpected that the particular components and configuration will varysubstantially from application to application depending on performancerequirements, cost constraints, etc. Moreover while certain currentconventional examples of such components have been described, it will beunderstood that the present invention can be used with other variants,advances, etc. of such components which are not yet well known and/orundiscovered. For illustrative purposes the present diagrams anddiscussion is simplified and skilled artisans will appreciate that othercomponents could be employed in deployed application.

Note that the size, shape and configuration of the components is merelyillustrative, and no assumptions or limitations should be drawn fromthese specific depictions. Accordingly the present disclosure will beunderstood by skilled artisans to describe and enable a number of suchvariants as well.

1. A method of transferring an epitaxial thin film comprising: providinga first frame portion with a body adapted to hold an assembly substrate;wherein said assembly substrate includes a plurality of openings adaptedto retain an epitaxial layer, and said plurality of openings extend froma top surface of said assembly substrate to a bottom surface thereof;providing a second base portion adapted to hold a seed substrate infixed contact with said assembly substrate; wherein said seed substratecan be used for growing said epitaxial layer within said assemblysubstrate from a liquid phase epitaxial material, and such that saidepitaxial layer contacts said seed substrate within said plurality ofopenings; controllably separating said first frame portion and saidsecond base portion so as to cause a separation of said epitaxial layerfrom said seed substrate; wherein said epitaxial layer can betransferred as a distinct layer from said seed substrate.
 2. The methodof claim 1, wherein said thin film epitaxial layer can be grownlaterally across a top surface of said assembly substrate.
 3. The methodof claim 1, further including a step: processing said assembly substrateand thin film epitaxial layer as an integrated epitaxial packagedstructure within a semiconductor processing apparatus to form activedevices on said assembly substrate and/or said thin film epitaxiallayer.
 4. The method of claim 1 wherein said thin film epitaxial layerincludes a graded composition throughout a thickness direction of saidassembly substrate.
 5. The method of claim 1 wherein said liquid phaseepitaxial material is adapted with thermal characteristics matching saidassembly substrate.
 6. The method of claim 1, wherein said separating isachieved at least in part by a shearing action.
 7. The method of claim1, wherein said separating is achieved at least in part by a chemicaletchant.
 8. The method of claim 1 further including a step: forming oneor more second separate thin film epitaxial layers on said thin filmepitaxial layer.
 9. The method of claim 1 further including a step:forming one or more second separate assembly substrates on said thinfilm epitaxial layer.
 10. The method of claim 10 wherein said one ormore second separate thin film epitaxial layers and said thin filmepitaxial layer include different dopant species.
 11. The method ofclaim 1 wherein said thin film epitaxial layer has a multidimensionalstructure including lines and via interconnects.
 12. The method of claim1, wherein said thin film epitaxial layer forms part of a p-n junction.13. The method of claim 1, wherein said thin film epitaxial layer formspart of an integrated circuit device.
 14. The method of claim 1 furtherincluding a step of forming a sacrificial layer attached between abottom surface of said assembly substrate and said surface of saidcrystalline substrate.
 15. The method of claim 1 further including astep of forming a spacer situated adjacent said assembly substrate andabove said crystalline substrate.
 16. The method of claim 1 furtherincluding a step: controlling heating and cooling of said liquid phasematerial.
 17. The method of claim 1 wherein said crystalline substratecan be re-used for growing a second epitaxial layer with said assemblysubstrate after said epitaxial layer is separated.
 18. The method ofclaim 1 further including a step: controlling a side profile of saidopenings to be vertical, step recessed or sloped to any desired angle.19. A method of transferring an epitaxial thin film comprising:providing a first frame portion with a body adapted to hold an assemblysubstrate; wherein said assembly substrate includes a plurality ofopenings adapted to retain an epitaxial layer, and said plurality ofopenings extend from a top surface of said assembly substrate to abottom surface thereof; providing a second base portion adapted to holda seed substrate in fixed contact with said assembly substrate; whereinsaid seed substrate can be used for growing said epitaxial layer withinsaid assembly substrate from a liquid phase epitaxial material which istemperature controlled such that said epitaxial layer contacts said seedsubstrate within said plurality of openings and grows from a bottomportion upwards; controllably separating said first frame portion andsaid second base portion, including with a heating process which is justbelow a re-melting temperature of the bulk of said epitaxial layer, soas to cause a separation of said epitaxial layer from said seedsubstrate; wherein said epitaxial layer can be transferred as a distinctlayer from said seed substrate.